Field of the Invention
The present invention relates to a fixing structure for a front design sheet secured to the front surface of a display unit with touch panel of an electronic apparatus or the like, and a display unit with touch panel.
Description of the Related Art
Generally, in a display unit with touch panel attached to an electronic apparatus or the like, a front design sheet is attached to its front surface to protect the main body of a touch panel, hide electrodes and the like around the touch panel, and provide outstanding design properties for the display unit (see Japanese Patent Applications Laid-Open Nos. 2009-277121 and 2007-241811).
An example of a conventional display unit with touch panel will be described with reference to FIG. 8.
A display unit 1 with touch panel includes a touch panel 2, LCD panel (liquid-crystal display device) 3, housing (bezel) 4, front design sheet 5, double-sided tape 6 for front design sheet fixation, and double-sided tape 7 for touch panel fixation.
The touch panel 2 is disposed above the LCD panel 3. The touch panel 2 is secured to a first step portion of the housing 4 by the double-sided tape 7 for touch panel fixation. The front design sheet 5 is disposed on the top of the touch panel 2. The front design sheet 5 is secured to a second step portion of the housing 4 by the double-sided tape 6 for front design sheet fixation.
FIG. 9 is a view showing a profile of the touch panel 2 of FIG. 8.
The touch panel 2 includes a light-transmitting upper film substrate and a light-transmitting lower glass substrate 10. A light-transmitting upper conductive layer 9, such as an indium tin oxide layer, is formed on the lower surface of the upper film substrate 8. Further, a lower conductive layer 11 is formed on the upper surface of the lower glass substrate 10.
A plurality of dot spacers (not shown) of an insulating resin are formed at predetermined dot pitches on the upper surface of the lower conductive layer 11. A pair of upper electrode layers 12A and 12B are formed individually on the opposite ends of the upper conductive layer 9. Further, a pair of lower electrode layers (not shown) extending perpendicular to the upper electrode layers 12A and 12B are formed individually on the opposite ends of the lower conductive layer 11. A substantially frame-shaped spacer (not shown) is disposed between the upper film substrate 8 and the lower glass substrate 10 so that the upper conductive layer 9 on the upper film substrate 8 and the lower conductive layer 11 on the lower glass substrate 10 face each other with a predetermined space therebetween. The touch panel 2 shown in FIG. 9 is constructed in this manner.
The upper electrode layers 12A and 12B on the opposite ends of the upper conductive layer 9 and the lower electrode layers on the opposite ends of the lower conductive layer 11 are connected to an electronic circuit (not shown) of an input device through a flexible printed wiring board (not shown). This flexible printed wiring board is formed by covering a wire of, for example, copper foil by an insulating film.
The display unit 1 with touch panel is configured so that if an operator depresses the upper surface of the upper film substrate 8 by his/her finger, pen, or the like while visually recognizing the display on the LCD panel 3 on the back of the touch panel 2, the upper film substrate 8 bends so that a depressed part of the upper conductive layer 9 comes into contact with the corresponding part of the lower conductive layer 11. Voltages from the electronic circuit are sequentially applied to the upper electrode layers 12A and 12B and the lower electrode layers. The electronic circuit detects the depressed part based on the voltage ratio between these electrodes so that various functions of the input device can be changed.
As described above, the front design sheet 5 is affixed to a molded housing in a manner such that a resin sheet (e.g., PET sheet) covers the entire surface of the display unit 1 with a double-sided adhesive tape from the front side. Since the front design sheet 5 with very low rigidity is affixed directly to the molded housing 4, the front design sheet 5 may sometimes be wrinkled or deformed due to a difference in thermal expansion coefficient, in case of a change of temperature in the installation environment.
For a reduction in size and better design properties of the display unit 1, it is preferable that the distance (denoted by reference numeral 13 in FIG. 8) from the contour of the display unit 1 to a display area is as short as possible. It is necessary, however, to provide a sufficient fixing area for adhesive fixation of the touch panel 2 and the front design sheet 5 to the molded housing 4, and the presence of the fixing area hinders the reduction of the contour of the display unit 1 with respect to the display area. Since it is necessary to provide a region in which the touch panel 2 is secured to the housing 4 and a region in which the front design sheet 5 is secured to the housing 4, as shown in FIG. 8, the distance 13 from the contour to the display area becomes inevitably long.
In order to solve this problem, in a display unit disclosed in Japanese Patent Application Laid-Open No. 2007-241811, a front design sheet is affixed to a molded housing with a metal sheet therebetween, whereby the front design sheet is prevented from being wrinkled or deformed. However, this technique has a problem that the necessity of the metal sheet or other interposed parts results in an increase in the number of parts. Since the front design sheet is configured to be secured to the housing, moreover, it is not conducive to a reduction of the fixing area in size.
Furthermore, the electrode layers and the like are exposed to an ambient atmosphere on the outer peripheral end surfaces of the touch panel. If the electrode layers are mounted on an insufficiently sealed housing, therefore, they may suffer electrolytic corrosion or rust due to dust or water in the ambient atmosphere, possibly causing trouble.